1. Field of the Invention
The present invention relates to a construction and method for inhibiting the formation of cracks in concrete slabs, and more particularly relates to the use of a ductile strip comprising cementitious material and hydrophilic and/or hydrophobic fibers. The ductile strip is directly bonded between adjacent concrete slabs.
2. Background Art
Reinforced concrete slabs have been widely used in modern transportation engineering, such as highway and airport pavements and bridge decks. Reinforced concrete slabs are also used in buildings, such as parking garage and factory or warehouse flooring. The average service life of a concrete slab is determined by many factors including the initial design details, material properties, traffic load and frequency, environment, salt application, and the presence and effectiveness of protective systems and maintenance practices, among others. All these factors influence the development of cracks in concrete slabs during their use. Cracking in slabs reduces the load capacity of the slab, and has been linked to fatigue failure. Cracking may cause deterioration in ridability and durability.
Concrete shrinkage and expansion is a principal reason for the initial formation of cracks in concrete slabs. As temperature changes occur, concrete expands or contracts, resulting in the formation of stresses in concrete slabs. For instance, an increase in temperature can cause the concrete slab to expand, resulting in compressive stresses in the slab as it bears against neighboring slabs or other structures. Alternatively, decreasing temperatures can cause the concrete slab to shrink, resulting in tensile stresses in the slab. As the tensile stress produced by temperature and shrinkage attains the tensile strength of concrete, cracking occurs in the slab. Concrete typically has a tensile strain capacity of about 0.01-0.02%. A typical transverse crack 4 in concrete pavements 6 is shown in FIG. 1. Deterioration of concrete slabs is a common cause requiring repair, rehabilitation or replacement of pavement and bridge structures. Therefore, innovative technology for repair and for new construction of concrete slabs is urgently needed.
At present, there is no cost-effective, reliable way of preventing the occurrence of the before-mentioned transverse cracks in concrete slabs. At present, the shrinkage and temperature change induced cracking of slabs is prevented in concrete pavements by making transverse joints, i.e., manually initiating discontinuities of the pavement by reducing the section of the pavement at the joints by 20 to 25%. These joints enable the slabs to move under shrinkage strain or temperature gradient. The distance between two closest joints is normally around 4 to 6 meters. These manually induced cracks (i.e., joints) often become the main source of pavement deterioration. In addition, this kind of construction can result in an uncomfortable motorist ride due to the discontinuity in the concrete slabs. Even with such joints, transverse cracks have been found to occur.
Accordingly, it would be desirable to have a reliable and cost-effective concrete construction and method of making or repairing a concrete construction that inhibits the formation of stress related cracks in concrete slabs, while avoiding problems associated with the prior art.
The present invention pertains to the preparation of cementitious structures wherein the effects of tensile and compressive forces are minimized without resort to artificial joints between concrete slabs. As a result, ingress of deteriorating substances (i.e., salt water) is considerably reduced, while the smoothness of the surface is not unduly compromised. The process involves directly bonding a ductile, fiber-reinforced cementitious xe2x80x9cexpansion stipxe2x80x9d between abutting concrete slabs or between a concrete slab and a supporting structure, i.e., a retaining wall, building wall, etc. The ductile strip useable with the present invention comprises an engineered cementitious composite of cementitious material and reinforcing fibers.